isNull{Fun,}Ptr

> Wolfram Kahl suggested to add functions isNullPtr and
> isNullFunPtr (with the expected semantics) to the Ptr
> module. Opinions?
Ptr and FunPtr are already instances of Eq, so which is easier to type?
isNullPtr x
or
x==nullPtr
So I don't see the motivation for the new predicates, but I don't have
any objections either.
Regards,
Malcolm